In neuroscience, we spend most of our time trying to understand the function of the “normal” brain — whatever that means — hence, we are most interested in the average. Under most occasions when scientists take an interest in the abnormal neurology, it is usually someone with who has something wrong with them — has brain damage or a disorder of some kind. In these cases, we try and understand what brain functions they have difficulty performing as a way to understand what each part of the brain does (and hopefully to someday be able to help them).
The point is that when neurologists study the abnormal, it is typically on the non-functional end of the spectrum rather than the highly functional. This is why I found a paper in the journal Neurocase quite interesting. The authors, Raz et al., placed a superior mnemonist — an individual who can memorize long lists of arbitrary items — into an fMRI scanner to try and get an idea how they did it.